The present invention relates to sensor technology. More particularly, the present invention relates to mechanisms for sensing such quantities and qualities as stress, strain, force, pressure and acceleration based on a change in electrochemically generated voltage with application of stress, strain, force, pressure or acceleration.
Sensors play a vital role in today""s technology. There is a great demand for sensors of stress, strain, force, pressure and acceleration. The mechanisms and methods that are usually used for sensing these qualities (and quantities thereof) include: piezoelectric, piezoresistive, capacitive and fiber-optic. These technologies have their advantages and disadvantages. The piezoelectric sensors rely on a generation of charges or a voltage when a stress or strain is applied. The piezoresistive sensors are based on a change in resistivity in a semiconductor with an applied stress or strain. The capacitive sensor relies on a change in capacitance as a stress or strain is applied on one of the electrodes of the capacitor thereby changing the separation of the electrodes. The fiber-optic sensors sense a change in light transmission through optical fiber when a stress or strain is applied. The best piezoelectric material is a solid solution of PbZrO3 and PbTiO3 (PZT) which is a ceramic material. PZT is not suitable for providing a sensor for a large area. It suffers another disadvantage in that PZT is a ceramic which is very brittle and subject to breaking. Piezoelectricity is a transient effect and produces little change if a constant stress or strain is applied. The ceramic material is brittle and relatively expensive. The polymer polyvinylidene fluoride (PVDF) is also a piezoelectric material but has a much smaller piezoelectric coefficient than PZT and both the ceramic and polymer materials need to be poled at a high voltage and high temperature to obtain the piezoelectric behavior, which increases the cost. Hence any large area ( greater than 1 cm2) application is expensive. The best piezoresistive material is silicon which is relatively expensive and brittle and the piezoresistivity is temperature sensitive. The capacitive sensors have high sensitivity but a smaller range of operation providing linearity. The fiber-optic sensors can be too sensitive to temperature fluctuation. In any case, the world market in sensors is expanding at a rapid pace and has already exceeded ten billion U.S. dollars. Novel sensor technologies providing highly sensitive, inexpensive and more versatile sensors than presently available can make an immediate impact in this market.